On Sat, 2020-04-25 at 13:42 +0200, Mateusz Holenko wrote:
> From: Pawel Czarnecki <pczarnecki@xxxxxxxxxxxxxxxxxxxxxxxx>
>
> This commit adds driver for the FPGA-based LiteX SoC
> Controller from LiteX SoC builder.
Sorry for jumping in late, Joel only just pointed me to this :)
> + * The purpose of `litex_set_reg`/`litex_get_reg` is to implement
> + * the logic of writing to/reading from the LiteX CSR in a single
> + * place that can be then reused by all LiteX drivers.
> + */
> +void litex_set_reg(void __iomem *reg, unsigned long reg_size,
> + unsigned long val)
> +{
> + unsigned long shifted_data, shift, i;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&csr_lock, flags);
> +
> + for (i = 0; i < reg_size; ++i) {
> + shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> + shifted_data = val >> shift;
> +
> + __raw_writel(shifted_data, reg + (LITEX_REG_SIZE * i));
> + }
> +
> + spin_unlock_irqrestore(&csr_lock, flags);
> +}
> +
> +unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_size)
> +{
> + unsigned long shifted_data, shift, i;
> + unsigned long result = 0;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&csr_lock, flags);
> +
> + for (i = 0; i < reg_size; ++i) {
> + shifted_data = __raw_readl(reg + (LITEX_REG_SIZE * i));
> +
> + shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> + result |= (shifted_data << shift);
> + }
> +
> + spin_unlock_irqrestore(&csr_lock, flags);
> +
> + return result;
> +}
I really don't like the fact that the register sizes & sub sizes are
#defined. As your comment explains, this makes it harder to support
other configurations. This geometry should come from the device-tree
instead.
Also this while thing is rather gross (and the lock will not help
performance). Why can't CSRs be normally memory mapped always instead ?
Even when transporting them on a HW bus that's smaller, the HW bus
conversion should be able to do the break-down into a multi-breat
transfer rather than doing that in SW.
Or at least have a fast-path if the register size is no larger than the
sub size, so you can use a normal ioread32/iowrite32.
Also I wonder ... last I played with LiteX, it would re-generate the
register layout (including the bit layout inside registers potentially)
rather enthousiastically, making it pretty hard to have a fixed
register layout for use by a kernel driver. Was this addressed ?
Cheers,
Ben.
